Use _Py_RVALUE() in macros (#99844)

The following macros are modified to use _Py_RVALUE(), so they can no
longer be used as l-value:

* DK_LOG_SIZE()
* _PyCode_CODE()
* _PyList_ITEMS()
* _PyTuple_ITEMS()
* _Py_SLIST_HEAD()
* _Py_SLIST_ITEM_NEXT()

_PyCode_CODE() is private and other macros are part of the internal
C API.